JPS6325061A - Printing control apparatus of thermal printer - Google Patents

Abstract

PURPOSE:To supply proper applied energy, by a method wherein the temp. characteristic of a thermistor is corrected by a resistor network to be amplified by an operational amplifier and the output potential of the operational amplifier is set as reference potential and the charging time up to the reference potential of a condenser is outputted as a pulse width by a voltage comparing circuit to be set to the reference current supply time of a heat generating element. CONSTITUTION:A resistor network 1 corrects the temp. characteristic of a thermistor. When the values of resistors 23, 24 are set to R23, R24, the value of a condenser 10 to C10 and the output potential of an operational amplifier to Vop, a pulse width TW is determined by the potential Vop. By selecting the values of C10, R23, R24 and the value of an amplifying circuit 2, a characteristic having the change ratio of the pulse width linear to temp. change in a limited temp. range can be realized. The output of a comparing circuit 9 is transmitted to a transistor 27 for switching through an inverter buffer 25. The transistor 27 is connected to the power source supply terminal 26a of a head driver 26 and the head driver 26 becomes operable only for the time of the pulse width TW and the reference current supply time of a heat generating element 30 is determined.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a printing control device for a thermal printer having a thermal head having a plurality of heat generating elements arranged thereon.

[Conventional technology]

In general, thermal printers produce density differences in printed dots due to the effects of ambient temperature and the self-heating of the thermal head itself, and the dot shape becomes distorted due to the trailing phenomenon, resulting in holes.

Next, conventionally, there is a method of converting a temperature change into a power supply voltage of a heating element as disclosed in Japanese Patent Application Laid-Open No. 54-56757, and a method as disclosed in Japanese Patent Application Laid-Open No. 59-7068.
Read the value of the head temperature detection means with an A-D converter, and
A method has also been proposed in which the read value is determined by a PU and the voltage applied to the head is determined by a DA converter.

[Problem that the invention seeks to solve]

These conventional examples had the following problems: 1. Generally, secondary heating resistors formed by sputtering of tantalum nitride or the like are extremely sensitive to overvoltage.
The method of varying the applied voltage in response to temperature changes requires extreme caution to prevent damage to the heating resistor.

IC, A-I) converter, D-A converter,
The device is large and expensive, and has not been used for serial printers, etc., and weighs 7 tons.

An object of the present invention is to provide a printing control device for a thermal printer for temperature compensation, which can supply appropriate applied energy in a wide temperature range in response to changes in the temperature of the thermal head and its surroundings. The aim is to realize these in a simple and low cost manner.

Another object of the present invention is to provide a printing control device that is safe against damage to the thermal head.

[Elaborate means to solve problems]

The print control device for a thermal printer according to the present invention has the following means.

(a) A thermal head or a heat-sensitive resistance element that detects the ambient temperature f'r (b) A resistance circuit network including the heat-sensitive resistance element, (C
) an amplifier circuit that amplifies the potential at a predetermined voltage division point of the resistor network; (d) a voltage comparison circuit that uses the output potential of the amplifier circuit as a reference potential and converts the charging and discharging time of the capacitor into a pulse width; (e) A power supply control circuit that sets the entire output time of the voltage comparison circuit as a reference energization time to the heating element on the thermal head.

[Effect]

The temperature characteristics of the thermistor are corrected by a resistance network that includes a thermistor, which is a kind of heat-sensitive resistance element that detects the temperature of the thermal head or its surroundings, and this is amplified by an operational amplifier, which is an amplifier circuit.The output potential of this operational amplifier is set as the reference potential. By outputting the charging time of the capacitor to this reference potential as a pulse width by the voltage comparator circuit and using this pulse width as the reference energization time of the heating element on the thermal head, it is possible to always maintain immunity against temperature fluctuations. Pulse width is added.

〔Example〕

FIG. 1 is a schematic circuit diagram showing an embodiment of the printing control device according to the present invention.

1 is a resistance circuit network including a thermal head or a thermistor 7 which is a type of heat-sensitive resistance element for detecting ambient temperature, 11 and 12 are resistors, and 13 is a capacitor for noise prevention. The capacitor 13 has no relation to the characteristics at all.

Reference numeral 2 denotes an amplifier circuit having an operational amplifier 8, which has, as inputs to the operational amplifier, a predetermined voltage dividing point of the resistor network and a predetermined voltage dividing point of a voltage dividing circuit 140 having a variable resistor 16t. The operational amplifier 8 also has a feedback resistor 19, a diode 20, and an input resistor 1st. The voltage dividing circuit 14 includes resistors 15, 17,
and a variable resistor 16, forming a reference input section of the operational amplifier 8.

3 is the voltage comparison section, is it a voltage comparison circuit? , capacitor 10,
It has resistors 25 and 24 and transistors 21 and 22 as basic components.

Reference numeral 4 denotes a power supply control circuit, which includes a buffer 25, a head driver 26, and a switching transistor 27.

5 is a thermal head having a heating resistor 50 which is a heating element.

6 is a CPU that centrally controls the thermal printer.

〔motion〕

The resistance network 1 is a curve correction section that corrects the temperature characteristics of the thermistor.

The resistance value Rt of the thermistor is generally 20 using the B constant.
It is expressed by the following formula, where the value of °C is R(20) and the absolute temperature T.

Rt=R(20) expB 1lJL-Eng)...Formula 1%Formula% Tt=Absolute temperature at any temperature T20=Absolute temperature at 20℃ Looking at equation 1, the following contains the eXp 0 term. Therefore, the reciprocal of temperature is 1 Of linear. i.e. resistance 1
[ decreases as the temperature rises, and the rate of change is smaller on the high temperature side.

In the case of a thermal head, it is necessary to reduce the applied energy when the temperature is high to obtain good print quality and to be safe for the heat generating element, and to correct the characteristics of this thermal head.

Figure 2 is a graph showing the characteristics of the resistance value Rt of the thermistor and the output voltage at the voltage division point A of the resistor network 1, where the horizontal axis is the absolute temperature, and the vertical axis is the resistance value Rt and the voltage division point. ! It shows the rank.

41 is a characteristic curve showing the temperature characteristic of the resistance value Rt of the thermistor, and 42 is a characteristic curve showing the temperature characteristic of the voltage dividing point AC)'[. The thermistor has negative characteristics with respect to temperature changes, as shown in the characteristic curve.

The features of this type of correction are as follows: (1) There are few peripheral elements and there are few fluctuations such as variations.

■ Linearity can be maintained over a relatively wide range.

■ Changes in the output voltage with respect to temperature outside the operating temperature range, for example below 0°C, above 40°C, etc., can be made small, and the thermal head can be protected from destruction.The amplifier circuit 2 uses corrected temperature characteristics. Partially expanded k, the partial pressure point A? obtains the characteristic curve 42'i? One input is used, and a voltage dividing circuit using a resistor is used as the other input.

The magnification of this circuit is expressed as follows.

If the value of the resistor 18 is fRIB and the value of the resistor 19 is R19, then the magnification is as follows.

The functions of the diode 20 are as follows: (1) To suppress a sudden rise in the reference potential at low temperatures, as a result, it prevents the output pulse width of the voltage comparison circuit 9 from increasing at low temperatures.

By using the characteristics of ■■ and changing the number of diodes, various characteristics -IJt- can be created.

The variable resistor 16 in the voltage dividing circuit 14 adjusts the output potential Vopt without changing the rate of change of the output potential with respect to temperature. This is used to set the initial value of the energy applied to the head.

The transistor 21 in the voltage comparator 3 is a discharging transistor that momentarily discharges the capacitor 10.

FIG. 3 is an explanatory diagram showing the input signal and output waveform of the voltage comparison section, and 51 is a trigger signal sent from 0PU6. 52 and 53 show the output waveforms, 52 shows the output when the pulse width switching transistor 22 is off,
Reference numeral 53 indicates the output when this is on. The pulse width TW1 of the output waveform 52 is larger than the pulse width TW2 of the output waveform 53. This switching of the pulse width is performed when the energy applied to the thermal head is changed depending on the characteristics of the ink ribbon, the surface condition of the printing paper, etc. to obtain favorable conditions.

This pulse width TV is determined by setting the values of the resistor 23 and the resistor 24 as R23 and R24, respectively, and the value of the capacitor 10 as ykC.
10 and the output potential of the operational amplifier is Top, when the transistor 22 is off, it is expressed as follows. At this time, the pulse width of the trigger input is extremely small, so it is ignored.

Also, when the transistor 22 is on, jln=
The natural logarithm VC is a circuit voltage that is generally constant at 5V, and the pulse width TV is determined by the potential of Vop.C10, R2
By selecting the values of 5 and R24 and the value 1 of the preceding stage amplifier circuit 2, it is possible to realize a characteristic having a rate of change in pulse width linear with temperature change within a limited temperature range. In addition, it is also possible to freely change the temperature characteristics.

The output of the voltage comparison circuit 9 is transmitted to the switching transistor 27 via the inverter buffer 25. The transistor 27 is connected to the power supply terminal 26a of the head driver 26, and the head driver is enabled to operate for the pulse width TV time. The reference energization time of the heat generating element 300 is determined.

Generally, in thermal history control etc., continuous communication to the heat generating element 50 is performed.
At times, a method is used in which the current supply time to the heating element is made to disappear for a predetermined period of time from the pulse @TW.

In this case, when the head driver 26 is in the operable state, the
The power supply time is reduced using the data output signal 6ajz from PtllIll.

VC and VH refer to the circuit power supply and the thermal head power supply, respectively.

Further, the diode 20 can be left in place when it is not needed, and can also be a Schenner diode.

Furthermore, using a thermistor as a heat-sensitive resistance element, the hole is
It is also possible to use a posister which has a positive temperature characteristic. At this time, the characteristics can be reversed by changing the input direction of the operational amplifier.

FIG. 4 shows another embodiment of the voltage comparison circuit of the printing control device according to the present invention.

60 is a one-shot timer C555, 61 is a control terminal and the input terminal of operational amplifier 8, 62 is a trigger input terminal, 63 is a resistor, 64 is a capacitor, 65
indicate the respective output terminals.

This output pulse width is also exactly the same as the characteristics of the voltage comparator circuit shown in FIG.

FIG. 5 is a characteristic diagram showing the relationship between applied energy and temperature of the thermal head obtained by the printing control device according to the present invention.

The applied energy E is the resistance 1fi-tRh of the thermal head.
, when the saturation voltage of the head driver is 78, it is expressed by the following equation.

The vertical axis in Figure 5 is this applied energy, and the horizontal axis is the temperature of thermistor 7! ', 71 represents the characteristic curve @I when the transistor 22 is off, and 72 represents the characteristic curve @I when the transistor 22 is on.

In this way, it is possible to maintain linear characteristics with respect to temperature changes, and the change in applied energy with respect to temperature is almost the same even when the transistor 22 is turned on or off. It is possible to stabilize against temperature changes.

〔Effect of the invention〕

According to the present invention, it is possible to have various temperature characteristics of energization time in accordance with the temperature characteristics required by a thermal printer.

In addition, it is possible to completely suppress the sudden increase in pulse width at low temperatures, which has a great effect on preventing the destruction of the heat generating element, and it is possible to always apply the appropriate energy and achieve excellent printing quality. It is possible.

Further, there is no need for expensive circuits such as A-D converters, and various applications are possible with simple circuits.

In addition to the heat-generating resistor element, the heat-generating element may also be an electrode-type printing element that generates heat in the resistance layer on the back side of the thermal transfer film using an electrode, which has the same effect.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an embodiment of a print control device for a thermal printer according to the present invention. FIG. 2 is an explanatory diagram showing the resistance value of a thermistor and the temperature characteristics of a voltage dividing point of a resistor network including the thermistor. FIG. 3 is an explanatory diagram showing input signals and output waveforms of the voltage comparison section. FIG. 4 is a diagram showing another embodiment of the voltage comparison circuit. FIG. 5 is a characteristic diagram showing the characteristics of the printing control device of the present invention. Thermistor 8... Operational amplifier 9... Voltage comparator circuit 30... Heat generating element Figure 2 Figure 3

Claims (3)

[Claims] (1) Has a thermal head with multiple heating elements arranged,
In a thermal printer that prints on plain paper via thermal paper or a transfer film, there is a heat-sensitive resistance element that detects the temperature of the thermal head or the ambient temperature, and the characteristics of the heat-sensitive resistance element are corrected, and the temperature of the heat-sensitive resistance element is A resistor network includes a resistor network, an amplifier circuit that amplifies the potential at a predetermined voltage dividing point of the resistor network, and a voltage comparison circuit that uses the output potential of the amplifier circuit as a reference potential and converts the charging and discharging time of the capacitor into a pulse width. A printing control device for a thermal printer, comprising: a power supply control circuit that sets the output time of the voltage comparison circuit as a reference energization time to the heat generating element. (2) While the amplifier circuit includes an operational amplifier as a component,
Printing by a thermal printer according to claim 1, wherein the input is a predetermined voltage dividing point of the resistor network, and the other input is a voltage dividing circuit using resistors including a variable resistor. Control device. (3) The printing control device for a thermal printer according to claim 1, wherein the heat-sensitive resistance element is a thermistor having negative characteristics with respect to temperature.